Considerable effort is being expended to develop wings capable of generating tractive force for the purposes of powering a user on a variety of vehicles that are tethered solely by flexible lines. Such wings can generally be considered kites. The development of kites capable of generating significant force has made possible numerous recreational pursuits. For example, kite surfing or kite boarding refers to a sport involving the use of a wind powered wing to pull the participant on a vehicle across a body of water. Similar sports involving the use of appropriately configured vehicles to traverse sand, earth, snow and ice are also being pursued. One of skill in the art will also recognize that wind powered wings can be used in any number of other applications, whether recreational or practical. With the development of these applications has come an increasing demand for kites having improved characteristics.
One type of kite that has achieved popularity is a leading edge inflatable (“LEI”) kite, typically comprising a semi-rigid framework of inflatable struts or spars that support a canopy to form the profile of the wing. This basic design is disclosed in U.S. Pat. No. 4,708,078 to Legaignoux, et al. The development of the LEI kite is generally credited with spurring the development of modern kite surfing due to its ability to be relaunched from the water's surface.
Most LEI kites currently employ four or five lines to control the kite. Two steering lines are attached at opposing ends of the kite at the trailing edge and at opposing ends of a control bar. Two front lines are attached at opposing ends of the kite at the leading edge and are secured to the middle of the control bar or to the user. The kite is steered by pivoting the control bar about a central axis to transmit force along the steering lines to the trailing edge of the kite. Further, by varying the relative length of the steering lines with respect to the front lines, the angle of attack of the kite can be adjusted, or “trimmed.” This has the effect of providing control over the amount of lifting force developed by the kite. Most kite control systems have a “fixed” adjustment mechanism for setting the trim of the kite by using a cleat, adjustable strap, or the like, which is positioned above the bar, meaning between the bar and the kite. Most control systems also provide “variable” dynamic trim adjustment by providing an attachment for the front lines to the user. Thus, the trim of the kite is constantly adjusted by moving the control bar in and out from the user's body. Kites employing a five line system have an additional control line secured to the leading edge between the kite tips. The fifth line helps maintain the shape of the kite and can allow the user to control a greater range of kite trim than possible using a four line system that is attached only to the tips.
As can be appreciated, LEI kites generally have a shape imparted by the inflated leading edge, the tension applied to the control lines and the aerodynamic forces experienced by the kite due to the movement of air across its surfaces. Although the inflatable leading edge is capable of contributing significant structure to the kite, there are practical limits related to the inflation pressure, the diameter of the leading edge and the strength of the materials. Accordingly, most LEI kites exhibit a pronounced arc shape caused by the balance between the force exerted by the control lines, which tend to bring the opposing edges together, and the structure imparted by the leading edge, which provides the effective lifting surface.
One drawback that has been observed with regard to the noted LEI kites is that the arc shape positions a substantial portion of the kite's surface in an orientation that is not perpendicular to the desired direction of the lifting force. Accordingly, attempts have been made to create a LEI kite that exhibits a flatter arc in flight, so that a greater proportion of the kite's surface is perpendicular to the lifting force, thus providing a more efficient airfoil. For example, U.S. patent application Ser. No. 11/067,842, which is hereby incorporated by reference in its entirety, discloses an LEI kite that has a flattened shape imparted by a bridle arrangement that distributes some of the control forces along the leading edge rather than at the tips. Kites having these general characteristics are known in the art as “bow” kites.
Bow kites offer certain advantages over conventional LEI kites. As noted above, the flattened arc profile improves the proportion of the kite's surface that generates lift in the desired direction. A further advantage is that bow kites can be designed to exhibit a wider range of trim than conventional LEI kites. To exploit the enhanced trim characteristics, bow kites typically require a relatively complex control bar having a pulley arrangement at either end for transmitting the steering forces to the kite. The 2:1 purchase ratio of these pulleys creates twice the relative change in length between the front lines and steering lines for a given amount of bar movement compared to a conventional control bar. As a result, the user has greater control over the lifting power developed by the kite.
The enhanced control corresponds to improved safety, as the user has greater ability to depower the kite, either when a mistake has been made or when the wind increases in strength. Another safety provision associated with bow kites is that the user's safety line can be attached to the same attachment point used to secure the front lines to the user, such as the chicken loop. This safety system allows the user to simply drop the bar while unhooked, and the kite will completely depower while the user is still attached via the safety line. Since they are capable of nearly complete depowering while in flight, bow kites offer obvious improvements in safety. The noted systems also have performance advantages in that the user can quickly optimize the power of the kite when desired, such as when jumping, without being overpowered at other times.
Despite the benefits of bow kites, the control systems suffer from a number of deficiencies. For example, to accommodate pulley travel, the steering lines are typically routed through the pulley and attached to the front lines at a point distal to the user. In turn, the fixed trim adjustment is conventionally positioned adjacent this point of attachment. As a result, many users cannot easily reach a fixed trim adjustment in this location. One attempt to overcome this problem is exhibited by the Cabrinha Crossbow Control System. This control bar employs extenders to help the user reach the fixed trim adjustment. However, this system adds to the already complex bar and can be difficult to operate given the increased play inherent in extending the control surfaces.
As can be appreciated, the location of the fixed trim adjustment is a problem that confronts more conventional control systems as well. To provide a variable sheeting function, an extension of the front lines is routed through the control bar before attachment to the user. This allows the user to sheet the bar in and out to dynamically vary the relative length of the front lines as compared to the steering lines, and thus trim the kite. However, the fixed trim adjustment is conventionally positioned on the front lines at a point beyond the sheeting range of the control system. Accordingly, the greater the ability to sheet the kite, the further the fixed adjustment system must be positioned away from the user.
Another drawback associated with bow kites is that increased trim range makes it relatively easy to inadvertently depower the kite more than desired. While this is not primarily a safety issue, it can negatively effect the use of the kite. For example, if the user inadvertently depowers the kite too much while riding, the loss of force can cause the user to stop planing which is obviously undesirable. Likewise, too much depower in the middle of a jump can lead to a loss of lift and an undesirably abrupt descent. These effects are exacerbated when the user is using only one hand. Further, it is essentially impossible to ride without hands using a conventional control system as the kite immediately depowers when the control bar is released.
Yet another drawback associated with bow kites and their conventional control systems is that the user must continually sheet in on the bar to maintain power in the kite. This can be tiring and reduce the amount of time the user is able to fly the kite.
Still another drawback relates to safety systems. For example, in the noted Crossbow Control System, an Override™ system includes a releasable stopper ball secured to the front lines. In normal use, the stopper ball keeps the control bar from being sheeted out beyond the normal range of trim. However, by pushing the control bar against the stopper ball, it can be dislodged and the control bar can be sheeted out to the maximum degree, completely depowering the kite. Unfortunately, this system has certain weaknesses. First, after the stopper ball is dislodged, it must be reattached at the desired position, which could be challenging depending upon the circumstances. Second, the system relies on a friction fit to retain the stopper ball in position and is accordingly susceptible to wear and variability in performance, for example, if it gets fouled with sand. Additionally, there is the risk of the system being inadvertently activated if the user drops the bar or attempts to ride without hands.
Accordingly, it is an object of the present invention to provide a control system for a kite that offers improved usability and performance.
It is also an object of the present invention to provide a control system for a kite that provides easy access to the fixed trim adjustment mechanism.
It is another object of the present invention to provide a control system for a kite with a safety system that fully depowers the kite.
It is yet another object of the present invention to provide a control system for a kite to easily limit the range of sheeting available while preserving the operation of the safety system.
It is also an object of the present invention to provide a method for controlling a kite that offers improved usability and performance.
Another object of the invention is to provide a method and system adapted to improve the control of a bow kite.
A further object of the invention is to provide a method and system for adjusting the fixed trim of a kite at a location proximal to the user from the control bar.
Yet another object of the invention is to provide a method and system for controlling a kite that provides improved adjustment of the dynamic sheeting range.